This invention relates to an apparatus for fixing radioactive and/or toxic waste materials obtained, for example, from nuclear installations. The apparatus is particularly designed for embedding aqueous concentrates, sludges and resins in a plasticizeable carrier material, such as hot bitumen. The apparatus has an extruder, as well as devices for the preparation, storage and the continuous, separated charging of carrier material and waste material into the extruder for mixing the materials. The extruder usually has two parallel-spaced horizontal shafts each carrying a screw conveyor passing through heating zones. Each heating zone has a vapor outlet device (vapor exhaust coupling) and a condenser, and after the condensers there is connected a common distillate accumulator. Each exhaust coupling is, at its upper end oriented away from the screw conveyors, closed by a window. With the extruder there are associated storage and/or transporting containers positioned, for example, on a rotatable disc for advancing the containers between the discharge spout of the extruder and the work zone of a conveying mechanism.
The production of nuclear energy is expected to sharply increase in the years ahead and thus necessarily one has to expect a substantial increase in the quantities of radioactive waste. These wastes have to be prepared in such a manner that the threat to the environment by residual radioactivities is excluded. It is noted that the quantities of liquid radioactive waste in a nuclear energy station are substantially greater than the quantities of solid wastes. Thus, the coolant circuit of a reactor is continuously contaminated by fission products and activated corrosion products so that a continuous purification is necessary. In addition, there is obtained radioactive waste water from the storage of fuel elements in water-filled containers and during the decontamination of reactor components and building structures. Further sources of radioactive waste water are leakages, laboratories and sanitary installations. The total waste water quantity in boiling water reactors is between 30,000 and 50,000 m.sup.3 a year and in case of pressure water reactors, between 15,000 and 20,000 m.sup.3 a year.
For decontaminating radioactive waste water in nuclear power installations several processes are used. Waste water having a relatively constant composition and small activity concentrations is treated by filtering through alluvial filters or by chemical precipitation. Empirical data show that this process yields 15 to 20 tons of residuals yearly. This volume, however, is substantially increased by the addition of inactive materials, such as filtering agents and precipitation reactants.
The purification of salt-poor waste water obtained from the reactor circuits and fuel element storage containers is effected almost exclusively by means of ion exchangers. The yield of ion exchange resin wastes is, dependent upon the type of reactor, between 10 and 20 m.sup.3 annually, with a specific activity in the order of magnitude of 10 to 500 Ci/m.sup.3.
The most universal and most effective process for the decontamination of radioactive waste water is vaporization. It finds application where larger quantities of waste water may be found which have a high activity in ion form bound to solid material. This process makes possible to increase the salt concentration of radioactive raw water up to approximately 30%.
The purpose of conditioning radioactive concentrates from the waste water preparation is to convert the final product into a storable, that is, a water-insoluble form.
Besides a mixing with cement up to a salt content of approximately 10 to 15% per weight, as a fixing method the substantially more advantageous embedding of aqueous concentrates or sludges or resins in hot bitumen is used. Here the fixation may be up to 60% by weight salt so that a 200 liter barrel may receive approximately 168 kg salt as opposed to 20 kg salt per barrel when the cementing process is used.
According to a known bitumenization process, the sludges or concentrates are introduced into the bitumen at a temperature of more than 140.degree.C by means of a dual-shaft extruder, whereby the water is evaporated and the radioactive salts are mixed with bitumen.
The above-outlined bituminization apparatus has a number of disadvantages which substantially increase the likelihood of malfunctioning and may require extensive maintenance work on heavily contaminated devices. Thus, for example, in the zone of the vapor exhaust device adjacent the screw conveyors of the extruder there are formed, during operation, deposits of radioactive salts which adversely affect the operation or even render it impossible because the resulting radiation limits the operational freedom of the maintenance or servicing personnel. The observation window at the upper end of the vapor exhaust device becomes obstructed after a relatively short period as a result of soiling by tar sprayers. The distillate produced in the condensers adjoining the vapor exhaust devices still carries bitumen particles which may adversely affect the operation of the evaporator unit. These particles must be removed in any event. from the distillate before its further processing to prevent organic material from entering the after-connected devices. Further, the loading of the mixture formed of bitumen and radioactive salts can be effected in the known apparatuses only by complex mechanisms which are thus prone to malfunctioning. In these known devices several containers are arranged on two rotary discs and to the discharge spout of the extruder there is attached a hose-like switchable device so that the mixed material emerging from the extruder can be, after filling one container on the first rotary disc, introduced without interruption into an empty container positioned on the second rotary disc.